Handheld, portable vacuum cleaners are known in which a two-stage filtration process, i.e. coarse filtration of air passing through the vacuum cleaner, followed by fine filtration, is carried out. A filter apparatus of a vacuum cleaner of this type is shown in FIGS. 1 to 4. A vacuum cleaner 2 has a housing 4 containing a motor (not shown) for driving a fan (not shown) having an air inlet 6. A filter apparatus 8 includes a coarse filter assembly 10 having a cup-shaped body 12 having apertures 14, and a resilient rubber seal 16 is provided around the periphery of the body 12. A pair of apertures 18, each of which comprises a smaller portion 20 and a larger portion 22, are provided on opposite sides of the periphery of the body 12, and resilient rubber seals 24 surround each aperture 18.
A fine filter assembly 26 comprises a body 28 having a shape corresponding to that of coarse filter assembly 10 and has a central aperture 30 in which a pleated filter element 32 of suitable fibrous material which will be familiar to persons skilled in the art is arranged. A pair of apertures 34, corresponding in shape to the apertures 18 at the periphery of coarse filter assembly 10, are provided on opposite sides of the periphery of body 28.
In order to assemble the filter apparatus comprising the coarse filter assembly 10 and fine filter assembly 26 and mount it to the housing 4 of the vacuum cleaner, the fine filter element 32 of the fine filter assembly 26 is placed inside the coarse filter assembly 10 such that apertures 34 overlie apertures 18, and the apertures 18, 34 are placed over corresponding pins 36 on housing 4. As can been seen particularly from FIG. 1, the pins 36 have enlarged heads which pass through the wider portions 22 of apertures 18, and the coarse filter assembly 10 is then rotated slightly relative to housing 4 to engage the shaft of pins 36 with the narrow portions 20 of apertures 18 to prevent removal of the coarse filter assembly 10, and thereby also of the fine filter assembly 26, from the housing 4. In this way, air entering into air inlet 6 is forced to pass through coarse filter assembly 10 and fine filter assembly 26 before it reaches the fan of the vacuum cleaner.
It would be desirable to provide a vacuum cleaner having the possibility of selection between single stage filtering and two stage filtering. For example, filtering via coarse filter assembly 10 and fine filter assembly 26 of the arrangement of FIGS. 1 to 4 involves more effective filtering but lower throughput of air than an arrangement in which the coarse filter assembly 10 is removed and only the fine filter assembly 26 is mounted to the housing 4. However, an attempt to provide single stage filtering (i.e. using only the fine filter assembly 26) in the arrangement of FIGS. 1 to 4 leads to a number of drawbacks. Firstly, apertures 34 of fine filter assembly 26 only prevent the passage of unfiltered dirt-carrying air when seals 24 surrounding apertures 18 of coarse filter assembly 10 are placed under compression. However, this can only occur when the coarse filter assembly 10 is also mounted to the pins 36, since the length of pins 36 and the presence of seals 24 around apertures 18 on coarse filter assembly 10 only means that when only the fine filter assembly 26 is mounted to pins 36, air containing dirt particles can enter air inlet 6 via apertures 34 without first passing through the fine filter element 32. This can lead to damage to the motor of the vacuum cleaner 2. Furthermore, because the apertures 18 on coarse filter assembly 10 and apertures 34 on fine filter assembly 28 are designed to be mounted to pins 36, it is possible for a user to mount coarse filter assembly 10 directly to housing 4 without fine filter assembly 28 being present. This can also lead to intake of air containing dirt particles into air inlet 6, leading to damage to the motor.
Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.